It seems that Nick knows about Eve as he is suspicious of Juliette's activities.

In the upcoming episode titled "Eve of Destruction" of "Grimm" Season 5, it seems Nick (David Giuntoli) will become suspicious of Juliette's (Bitsie Tulloch) behaviour and might find out about Eve's secret.

In the mid-season finale episode, titled "Wesen Nacht", Juliette returned, but her body has been possessed by Eve now. According to TV Line, she is "a mysterious woman working with Hadrian's Wall." The character has access to Juliette's mind. However, she lacks Juliette's usual emotional behaviour.

In an interview with the website, Tulloch said Eve's personality is now a little bit more dramatic as she can't be seen by anybody who has witnessed Juliette's death.

"I started watching Alias over the summer, because I was like, 'All right, she's got to be incognito.' That's been really fun — skintight leather and these awesome wigs that she wears whenever she's out," she said.

Enstarz has reported Eve is going to be "Hadrian Wall's most prized weapon" in the battle against the Black Claw.

David Greenwalt and James Kouf, co-creators of the series, told TV Line Eve would have a big scene with Nick. Greenwalt said Nick would eventually realise Eve is entirely different from Juliette and fans are eagerly waiting to watch the confrontation in the next episode.

The synopsis of the upcoming episode, as mentioned by TV.com, reads: "The surprise return of "Juliette" sends Nick on a quest for the truth. Trubel has information that could be valuable. Monroe and Rosalee turn to the Wesen Council for answers as the uprising escalates."

Whether Nick find out the truth behind Juliette's odd behaviour will be revealed only in the next episode.

"Grimm" Season 5 Episode 7, titled "Eve of Destruction", will air on 22 January, 2016, on NBC.